Radio communication device and semiconductor integrated circuit device used for the same

ABSTRACT

A semiconductor integrated circuit for a radio communication terminal sequentially uses a plurality of frequency channels by instructions from a hopping frequency decision unit to receive packet data by a reception unit. When the integrated circuit cannot detect the head of the packet data in reception operations, the integrated circuit cannot receive packet data should be received originally then assumes that the received packet data is a packet error. And the integrated circuit calculates packet error rates for each frequency channel on the basis of the number of times of reception operations performed for each frequency channel and of the number of times of packet errors to estimate channel qualities by using the packet error rates.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/331,820, filed Jul. 15, 2014, which in turn is a continuation of U.S.application Ser. No. 13/775,840, filed Feb. 25, 2013, which is adivisional of U.S. application Ser. No. 12/500,755, filed Jul. 10, 2009,which is a divisional of U.S. application Ser. No. 11/340,853, filedJan. 27, 2006, which is based upon and claims the benefit of priorityfrom prior Japanese Patent Application No. 2005-019980, filed Jan. 27,2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a radio communication device and asemiconductor integrated circuit used for the same. More specifically,the present invention relates to a radio communication device employinga channel quality estimation method, a method for deciding a channel tobe used and a method for deciding transmission power in a radio datacommunication of a frequency hopping system and relates to asemiconductor integrated circuit device used for the same.

2. Description of the Related Art

In recent years, a new radio communication system to connect electronicappliances with one another by radio has been developed. The IEEE802.11b/g, Bluetooth (trade mark) and the like are known as this kind ofradio communication system.

The IEEE 802.11b/g is a standard of a short-range radio communicationsystem proposed for a wireless local area network (LAN). The Bluetoothis a standard of a short-range radio communication system proposed forconnection among not only computers but a variety of appliances with oneanother. In these radio communication systems, the 2.4 GHz band calledan industrial scientific and medical band (ISM band) is used as afrequency band allowed to be freely used without any license on acondition that a prescribed standard is satisfied. The IEEE 802.11b/gadopts a direct sequence spread spectrum (DSSS) technology so as tomaximize influences of noise signals generated from other electronicappliances, for example, electronic ovens or the like present in the ISMband of the 2.4 GHz band. The Bluetooth adopts a frequency hoppingspread spectrum (FHSS) technology of the frequency hopping system. Eachtechnology, then, achieves sufficient noise-resistance for the radiocommunication system.

More specifically, a Bluetooth-compatible portable device (hereinafter,referred to as Bluetooth device) is used to exchange data among acellular phone, a personal digital assistant (PDA), a notebook personalcomputer, a sound terminal appliance, etc. In this case, the frequencyhopping system is adopted, wherein one channel is selected from among 79frequency channels defined in a frequency band from the 2.40 GHz to the2.48 GHZ and it is switched with the lapse of time to make a radiocommunication. This frequency hopping system repeatedly selects channelsat every fixed time period, for example, at every 625 μs on the basis ofa preset pseudo random algorithm and assigns one packet of data to theone channel to make a communication. On the other hand, a wireless LANstation using the 2.4 GHz band does not employ frequency hopping butemploys a constantly fixed and set frequency band, namely, contiguousfrequency widths equivalent to almost 20 channels of the Bluetoothdevice.

FIG. 1 shows frequency relationships when the Bluetooth device and thewireless appliance use the ISM band of the 2.4 GHz. The Bluetoothdivides almost entire areas of the ISM band of the 2.4 GHz into 79channels of 1 MHz width and communicates while sequentially changing thefrequencies used by the 79 channels at every 625 μs in accordance with apreset sequence defined by appliance addresses or the like.

On the other hand, the wireless LAN defines total 13 channels in the ISMband of the 2.4 GHz. A band width occupied by the one channel is 20 MHzand these 13 channels are arranged in a manner that a part of them areoverlapped one another, as shown in FIG. 1. Any one channel is assignedto each access point of the wireless LAN at the time of setting thereof,and communications are made by suing the assigned channels. Theinfluences of the noise signals are reduced by employing the DSSSsystem. Channels are assigned to each access point so as not interferewith one another when a plurality of access points are arranged in orderto overlap mutual service areas.

As shown in FIG. 1, presence of the Bluetooth device and the wirelessLAN appliance in an identical frequency area causes a mutualcommunication to be interfered by radio waves transmitted from eachother. To meet this interference, the Bluetooth device adopts anadaptive frequency hopping (AFH) technology. The AFH technology preventsthe interference between the Bluetooth device and wireless LAN appliancein a manner that the Bluetooth device observes the channels in anymethod to avoid the channel to be determined the presence of a radiowave to interfere its own communication and performs the frequencyhopping.

To achieve the AFH, it is needed for the Bluetooth device to observestates of each channel and determine which channel should be used.Therefore, it is expected to adopt a method for estimating channelquality and method for deciding a channel to be used which decides thefrequency to be used so as to avoid, with an appropriate response speed,use of channels with poor qualities by detecting channels surelyinfluenced from others, namely channels with bad in quality. TheBluetooth device is frequently adapted to a small sized appliance with asmall battery capacity such as a cellular phone and a head set needed tominimize its consumption current. The Bluetooth device also needs toavoid increase, as much as possible, in the consumption currentresulting from the adaptation of the method for estimating the channelquality and the method for deciding the channel to be used.

In general, a method for a certain radio appliance to estimate a qualityof channel to be used by itself includes a method for measuring a fieldstrength of a radio wave present in the channel to be used prior to acommunication (Passive method) and a method for assuming that thequality of the channel is poor when error rates of user data and controldata in communication exceed preset values (Active method).

The former Passive method directly measures the filed strength, so thatthe Passive method can quickly detect interference from otherappliances. However, since the radio appliance has to perform receptionoperations other than receptions of the user data and the control data,the consumption current is increased. A variety of error correctiontechnologies are introduced into packets of the Bluetooth and if theinterference is minor, the technologies can be suppressed affections ofthe interference by means of those correction technologies. But, in thecase of the Passive method, it is impossible to know the degree of theactual affections of the measured radio waves affected oncommunications.

On the contrary, since the latter Active method detects the influencefrom other radio appliances by measuring the error rates of the userdata and control data, the Active method has some advantages. That is,it is determined whether the influence is serious or not by addingactual affections of radio waves from interference sources on thecommunications, and the consumption current is not increased because theradio appliance does not receive other than the user data and controldata. However, the Active method has problems such that a plurality ofitems of data has to be received to measure the error rates and it takesa long time to determine each channel condition. And the Active methodfurther has a problem that interference waves are varied in strengthwith the elapse of time. The variations due to the elapse of time arecaused because a radio wave propagation environment is varied with theelapse of time (fading phenomenon) or the use of channels is originallybursty like the wireless LAN. Since the strengths of the interferencewaves vary as the time goes on because of those causes, this variationsof affections by the interference are also generated as a problem.

Furthermore, on the case of avoidance of use of channels with very poorqualities by means of the AFH, when qualities of most of channels in theISM band become poor, it is worried that radio waves to be transmittedfrom the Bluetooth are collected to a part of the ISB band to influenceadverse effects on other appliances.

The fact that it is possible for an evaluation of a channel quality of aradio communication using the AFH to use a bit error rate, a packeterror rate, a signal to noise ratio (S/N) or the like is disclosed inJapanese Patent No. 3,443,094.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided asemiconductor integrated circuit device comprises a hopping frequencydecision unit which selects one frequency channel from among theplurality of frequency channels; a transmission unit which assignspacket data to the selected frequency channel to+ transmit it; areception unit which receives the packet data of the selected frequencychannel; a error detection unit which assumes that there are packeterrors incapable of receiving the packet data to be originally receivedbecause of deterioration of a channel quality if a head of the packetdata could not be detected at the time when the reception unit performedreception operations of the packet data; and a control unit whichestimates channel qualities of the frequency channels received by thereception unit, and which makes the hopping frequency decision unitperform frequency hopping, first by calculating packet error rates foreach frequency channel on the basis of the number of the receptionoperations of the packet data and the number of the packet errorsdetected by the error detection unit, secondly by estimating channelqualities by using the packet error rates, thirdly by determiningwhether or not the received frequency channels are usable on the basisof a result of estimation of the channel qualities, and fourthly byavoiding the frequency channels determined to be unusable.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an exemplary view showing an example of frequencies to be usedby a Bluetooth device and a wireless LAN appliance;

FIG. 2 is a block diagram of a radio communication system showing aBluetooth device regarding a first embodiment of the invention togetherwith an access point of a wireless LAN;

FIG. 3 is a block diagram showing a configuration of the Bluetoothdevice in FIG. 2;

FIG. 4 is a block diagram showing a configuration of a semiconductorintegrated circuit device focusing attention on a functional aspect of aCPU in FIG. 3;

FIG. 5 is a flowchart showing a basic transmission procedure executed,under control through a transmission/reception control unit in FIG. 4,for transmitting packet data;

FIG. 6 is a flowchart showing a basic transmission procedure executed,under control through transmission/reception control unit in FIG. 4, forreceiving packet data;

FIG. 7 is a flowchart showing a field strength measuring procedureexecuted under control by transmission/reception control unit in FIG. 4;

FIG. 8 is a flowchart showing a basic procedure deciding a channel to beused, executed under control by transmission/reception control unit inFIG. 4;

FIG. 9 is a flowchart showing a reception procedure executed, by theBluetooth device in the first embodiment, for receiving packet data;

FIG. 10 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in the first embodiment;

FIG. 11 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in a second embodiment;

FIG. 12 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in a third embodiment;

FIG. 13 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in a fourth embodiment;

FIG. 14 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in a fifth embodiment;

FIG. 15 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in a sixth embodiment;

FIG. 16 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in a seventh embodiment;

FIG. 17 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in an eighth embodiment;

FIG. 18 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in a ninth embodiment;

FIG. 19 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in a tenth embodiment;

FIG. 20 is a flowchart showing a procedure deciding transmission power,executed by the Bluetooth device in an eleventh embodiment;

FIG. 21 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in the eleventh embodiment; and

FIG. 22 is a flowchart showing a procedure deciding a channel to beused, executed by the Bluetooth device in a twelfth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described through embodimentsby referring to drawings. In description, common parts are denoted bycommon reference numerals all over the drawings.

First Embodiment

FIG. 2 is a block diagram of the radio communication system showing theBluetooth device regarding the first embodiment of the inventiontogether with the access point of the wireless LAN. The radiocommunication system shown in FIG. 2 shows two devices of first andsecond Bluetooth devices 11, 12 as each Bluetooth device; however, thenumber of the Bluetooth devices is not limited to two. The radiocommunication system in FIG. 2 includes an access point 13 of thewireless LAN other than the first and second Bluetooth devices 11, 12and FIG. 2 shows a state in which a mutual radio communication betweenthe first and second Bluetooth devices 11, 12 is interfered by a radiowave from the access point 13.

The first and second Bluetooth devices in FIG. 2 includes asemiconductor integrated circuit device 20 (hereinafter, referred to asLSI) for Bluetooth integrated into one chip, a radio antenna 31connected to the LSI 20 and a host 32, as shown in FIG. 3, respectively.A transceiver/receiver circuit 21 including a high-frequency (RF)circuit, an AD conversion circuit, a memory 22 consisting of a ROM andRAM to store firmware including a protocol stack, a CPU 23 and aperipheral circuit 24, and the like are integrated in the LSI 20. Thetransceiver/receiver circuit 21 connects the radio antenna 31 theretoand the peripheral circuit 24 connects the host 32 thereto.

The Bluetooth device shown in FIG. 3 is built in a device to perform aradio communication. An example for the device to perform the radiocommunication includes, for example, a cellular phone, a car navigationsystem, a car audio device, a personal computer, a personal digitalassistant (PDA), a Bluetooth adapter, radio headset, a portable audiodevice, a digital camera, a printer, a cordless phone, a cordless mouse,a cordless keyboard, a gate controller, a general household electricappliance, and the like.

The Bluetooth device shown in FIG. 3 transmits and receives data andcommands between the memory 22 and the host 32 via the peripheralcircuit 24 under control by the CPU 23 and transmits data for atransmission stored in the memory 22 to the transceiver/receiver circuit21 to transmit it as radio waves from the radio antenna 31. On the otherhand, reception data is generated from the radio waves received throughthe radio antenna 31 and stored in the memory 22 then transmitted to thehost 32 via the peripheral circuit 24.

FIG. 4 is a block diagram showing the configuration of the LSI 20focusing attention on the functional aspect of the CPU 23 in FIG. 3. Thecircuit shown in FIG. 4 includes a transmission unit 41, a receptionunit 42, a transmission/reception control unit 43, a hopping frequencydecision unit 44 and a higher layer protocol processor 45. The radioantenna 31 is connected to the transmission unit 41 and the receptionunit 42. The reception unit 42 has a packet data reception unit 46, afield strength measuring unit 47 and an error detection unit 48.

The Bluetooth devices 11, 12 in FIG. 1 are modules to perform radiocommunications based on the Bluetooth Specification released by theBluetooth SIG and make communications by using the ISM band of 2.4 GHzband. The radio communication system of the Bluetooth Specificationutilizes a spectrum diffusion communication of a frequency hoppingsystem. The ISM band of the 2.4 GHz band is divided into 79 frequencychannels (hereinafter, referred to as communication channel) with 1 MHzintervals, and channels to be used are switched on a time-division basisfor each one time slot, based on the hopping patterns (frequencyhopping). The radio communication system of the Bluetooth Specificationadopts a master/slave system and a master manages the hopping patterns.The radio communication system can communicate by forming a radionetwork referred to as a pico-net among one master and slaves of maximumseven sets by using the same hopping pattern.

The LAN module at the access point 13 of the wireless LAN performs radiocommunications on the basis of the IEEE 802.11b standard and, likewisethe Bluetooth device, performs communications by using the ISM band ofthe 2.4 GHz band. The radio communication system of the IEEE 802.11bstandard utilizes a spectrum diffusion communication of a directdiffusion system. Thirteen frequency channels are assigned to thefrequency band of the 2.4 GHz band with intervals of 5 MHz extent, andmore than one arbitrary frequency channel among thirteen channels can beselected to be used. Forms of the radio networks include an Adhocnetwork to be used for communications among radio stations in an areacalled a basic service area (BSA) and an infrastructure network composedof a plurality of radio terminals and access points (AP). To preventsignal collisions on the radio network, a carrier sense/collisionavoidance function called CSMA/CA is provided.

In the first embodiment, the Bluetooth devices 11, 12 respectively havetransmission/reception control units 43 as communication channel controlunits so as to prevent interference between the radio communication ofthe foregoing IEEE 802.11b standard using the same radio frequency bandand the radio communication of the Bluetooth Specification. Thecommunication channel control unit of the Bluetooth device finds out acommunication channel interfering with other radio communication systemsuch as the IEEE 802.11b from among communication channels employed bythe Bluetooth device to stop the use of the communication channel andperforms control to release the stopped communication channel for otherradio communication system. The memory 22 in FIG. 3 stores data of thefrequency channel determined to be usable.

Having described the case where the Bluetooth device shown in FIG. 3achieves each circuit function shown in FIG. 4 by software processingusing the CPU 23, the circuit functions can be achieved by configuringeach circuit with the use of hardware.

The Bluetooth device performs communication control, from the managementof the hopping patterns down, is wholly initiated by the master,monitors a packet error rate (PER) and determines an influence channelonly on a master side, and can notify the stoppage of the use of thecommunication channel determined as the interference channel from themaster to the slave.

Since the processing of the hopping control or the like in the Bluetoothdevice is performed by a protocol stack on a base band unit, thefunction of the aforementioned communication channel can be installed inthe protocol stack of the base band unit. A packet error becoming asource to calculate the PER is detected from the error detection unit 48in the reception unit 42 and received power is measured by the fieldstrength measuring unit 47.

The communication channel control unit of the wireless LAN module doesnot have a function of finding out the communication channel interferingwith other radio communication system such as the Bluetooth from amongeach communication channel used by the LAN module to stop the use of thecommunication channel and performing control to release thecommunication channel to other radio communication system.

Next to this, basic functions owned by each unit shown in FIG. 4 will bedescribed schematically.

The higher layer protocol processor 45 performs assembly/disassembly ofa packet, creates a packet of a Bluetooth link level from data to becommunicated to transfer it to the transmission unit 41 and reproducesthe data from the received packet having the Bluetooth link level.

The hopping frequency decision unit 44 selects one frequency channel tobe used for radio communications from among a preset plurality offrequency channels and instructs the selected frequency channel with thelapse of a time.

The transmission unit 41 receives the packet data items from the higherlayer protocol processor 45. The unit 41 allocates these data items therespective frequency channels sequentially selected by the hoppingfrequency decision unit 44. The unit 41 then transmits the packet dataitems, one by one.

The packet data reception unit 46 in the reception unit 42 receivespacket data of the frequency channels sequentially instructed by thehopping frequency decision unit 44. The field strength measuring unit 47measures strengths of reception fields of the frequency channels. Whenthe head of the packet data could not be detected in the receivingoperation by the packet data reception unit 46, the error detection unit48 assumes this situation as a packet error in which packet data to bereceived originally cannot be received due to deterioration in channelquality.

The transmission/reception control unit 43 determines whether performsany one of a transmission operation, a reception operation and a fieldstrength measuring operation at every slot each having 625 μs lengthdefined by the Bluetooth or does not perform any of them. Thetransmission/reception control unit 43 instructs to the transmissionunit 41, reception unit 42 and hopping frequency decision unit 44 andcontrols them to operate any one of the operations among each step shownin FIG. 5 to FIG. 8.

Next to this, in the radio communication system including the first andsecond Bluetooth device 11, 12, a summary of an example for a series ofprocedures to make radio communications will be taken to be explained.

The Bluetooth Protocol decides one device operating as a master amongtow or more devices performing communications and makes the master sidedevices control data transmissions from devices operating as slaves.Here, the case where the first Bluetooth device 11 becomes a master sideand the second Bluetooth device 12 becomes a slave side will be taken asan example to be described.

At first, the Bluetooth device 11 performs inquiry and paging inaccordance with the Bluetooth Specification to find out the secondBluetooth device 12. After this, the first Bluetooth device 11establishes a connection toward the second Bluetooth device 12 totransfer user data thereto by using the connection.

After proceeding this series of procedures, the summary of operations ofthe Bluetooth device in actual communications of the user data isdescribed as follows. In this case, the first and second Bluetoothdevices 11, 12 operate similarly.

The higher layer protocol processor 45 creates the packet with theBluetooth link level from data to be transferred. The packet istransferred to the transmission unit 41 to be transmitted through afrequency specified by the hopping frequency decision unit 44. On theother hand, during the establishment of the connection, the receptionunit 42 receives the frequency specified by the hopping frequencydecision unit 44 to reproduce the packet and transfers it to the higherlayer protocol processor 45.

Sending of radio waves from the access point 13 of the wireless LANlocated in the vicinity of the Bluetooth device causes mutualcommunications between the Bluetooth devices 11 and 12 to be influenced.This fact is recognized as an increase in an error inspection rate bythe error detection unit 48 included in the reception unit 42 and anincrease in field strength of a channel not expected by the Bluetoothdevice. Based on the information with respect to the above-mentionedrecognition, the hopping frequency decision unit 44 detects interferencebetween the Bluetooth device and the access point 13 of the wireless LANto decide a channel to be used.

From FIG. 5 to FIG. 8 are the flowcharts schematically showing each oneexample of basic operations of the Bluetooth device shown in FIG. 4.FIG. 5 is an exemplary flowchart showing a transmission procedure whenthe transmission unit 41 of the Bluetooth device transmits packet data,FIG. 6 is a flowchart showing a reception procedure when the receptionunit 42 receives the packet data, FIG. 7 is a flowchart showing a fieldstrength measuring procedure when the field strength measuring unit 47measures a field strength, and FIG. 8 is a flowchart showing a decisionprocedure of a channel to be used when the hopping frequency decisionunit 44 decides a channel to be used.

The Bluetooth standards define a time slot with a length of 625 μs. Thetransmission/reception control unit 43 of the Bluetooth devicedetermines whether any one of the transmission operation, receptionoperation and field strength measuring operation at every slot should beperformed or none of them should be performed. Thetransmission/reception control unit 43 then issues instructions to thetransmission unit 41, reception unit 42 and hopping frequency decisionunit 44 to make them execute operations of each step shown in any ofFIG. 5 to FIG. 8.

(A) Basic Operations in the Transmission of the Packet Data (Flowchartin FIG. 5)

When the transmission of the packet data is started (step S51), atfirst, the hopping frequency decision unit 44 instructs the transmissionfrequency to the transmission unit (step S52). The transmission unit 41modulates, with the specified frequency, the packet data supplied fromthe higher layer protocol processor 45 to transmit it (step S53). Whencompleting the transmission of the supplied packet data, thetransmission unit 41 terminates the transmission operation (step S54).

(B) Basic Operations in the Reception of the Packet Data (Flowchart inFIG. 6)

When the reception of the packet data is started (step S61), at first,the hopping frequency decision unit 44 instructs the reception frequencyto the reception unit 42 (step S62). The reception unit 42 performs apacket reception operation with the specified frequency. Specifically,the reception unit 42 receives a radio wave of the specified frequencyto demodulate it (step S63). After this, the reception unit 42 searchesSync Word of a preset pattern from the demodulated data to detect thehead of the packet data (step S64). When detecting the head of thepacket data, the reception unit 42 proceeds to a step S65. If thereception unit 42 could not find a packet, the reception unit 42proceeds to a step S70 and updates error information showing the factthat synchronization detection could not be completed to terminate thereception operation. If the head of the packet data could be detected,the error detection unit 48 performs error detection/correction of aheader section by using error detection/correction codes included in theheader section in the step S65. Wherein, if an error exceeding anability of the error detection/correction code is detected, thereception unit 42 proceeds to a step S70 to update error informationshowing the fact that a header error was detected but the error couldnot be corrected then terminate the reception operation.

When any error was not found in the header section or even when theerror was found but it was corrected successfully, the error detectionunit 48 detects the error of data section in a step S66. In this case,at first, the detection unit 48 refers to information included in theheader section to recognize the packet type. In the case of theBluetooth, error detection/correction codes to be used are set up foreach packet type and the reception unit 42 conducts the errordetection/correction operation for data section in accordance with thecodes. When an error was not detected or even when the error wasdetected but it was corrected successfully, the step S66 shifts to astep S67. When the error was detected and it could not be correctedcompletely, the step s66 shifts to the step 70 then updates the errorinformation showing the fact that the error was detected but it couldnot be corrected to terminate the reception operation. Further, some ofthe packet types do not include the error detection/correction codes inthe data sections. Such types of the packets are not performed to detecttheir errors in the data sections and the step S66 shifts to the stepS67.

As the result of the error inspection for the data section, if the errorwas not detected or even if it was detected but corrected successfully,the reception unit 42 refers to the measurement result from the fieldstrength measuring unit 47 to update field strength information of acarrier wave by which the packet now in receiving has been carried (stepS67). The measuring unit 47 measures the strength of radio wavedemodulated in the step S63 in accordance with a prescribed method toupdate its value. The measuring unit 47 can adopt a variety of types offield strength measuring methods therefore; however the types do notaffect any influence onto effectiveness of the present invention, sothat the description about the reception operation will be continuedwithout any limitation.

At the last step of the reception operation, the reception operationtransfers the packets which were processed thereby up to now to thehigher layer protocol processor 45 (step S68) and terminates itself(step S69).

(C) Basic Operations in the Field Strength Measurement (Flowchart inFIG. 7)

When the field strength measurement is started (step S81), at first, thehopping frequency decision unit 44 instructs a frequency to measure thefield strength (step S82). The field strength measuring unit 47 measuresthe field strength of the instructed frequency, and when completing themeasurement, the reception unit 42 refers to the measured value from themeasuring unit 47 to update field strength information (step S83).Concluded, the field strength measurement unit 47 is terminated (stepS84).

(D) Basic Operations in the Decision of the Channel to be Used(Flowchart in FIG. 8)

The operations in the decision of the channel to be used is differentfrom the foregoing transmission operation, reception operation and fieldstrength measuring operation and not performed at every 635 μs slot. Butthe operations are instructed to be executed with a pre-determinedinterval, for example, 10-second interval, by the transmission/receptioncontrol unit 43 of the Bluetooth device in order to control theoperations of the hopping frequency decision unit 44. When the decisionoperation of the channel to be used is started in accordance with theinstruction from the transmission/reception control unit 43 (step S91),the hopping frequency decision unit 44 refers to the error informationstored in the error detection unit 48 and the field strength informationstored in the field strength measuring unit 47 (step S92). The hoppingfrequency decision unit 44 then estimates a channel quality on the basisof the acquired information to decide the channel to be used (step S93).At last, the hopping frequency decision unit 44 notifies the channel tobe used to the Bluetooth device on the other party (step S94) toterminate the operations (step S95).

The operations to decide the channel to be used are conducted by themaster side device in accordance with the Bluetooth Protocol. In thestep S94, information on the channel decided to be used is notified fromthe master side device to the slave side device.

As mentioned above, the operations in the steps S64, S65 and S66 in FIG.6 are those that the reception unit 42 reproduces a packet from thereceived radio wave. If the channel quality of the channel which hastransmitted the packet is deteriorated, the possibility of occurrence ofa failure in a reproduction of the packet increases. When the receptionunit 42 failures to reproduce the packet from the radio wave received ata certain slot, types of failures are considered as follows.

(A) Synchronization Error (Sync Error)

This error occurs when the retrieval of the Sync Word executed in thesynchronization detecting step (step S64) times out. In this case, thepacket is not detected.

(B) Header Error

This error occurs when an error is detected in the header errorinspection step (step S65) and the error exceeds the ability of thecorrection code. In this case, the packet is discarded.

(C) Data Section Error

This error occurs when an error is detected in the data section errorinspection step (step S66) and the error exceeds the ability of theerror correction code. In this case, the packet is discarded.

When these errors occur, the information is classified and stored foreach error type and for each channel to be used in the error informationupdate step (step S70) to be used in the decision operations of thechannel to be used.

For the Bluetooth device in the first embodiment, the followingfunctions achieved through software by the CPU 23 by using the programstored in the memory 22 in FIG. 3 is added to the transmission/receptioncontrol unit 43.

(1) Channel Quality Estimation Function

This function calculates packet error rates for each packet from thenumber of times of packet data reception operations conducted for eachfrequency channel and the number of times of packet errors detected fromthe error detecting unit 48 when estimating each channel quality of thefrequency channels received from the packet data reception unit 46 andestimates channel quality by using the packet error rates.

(2) Frequency Channel Selection Function

This function determines whether or not the frequency channel is usableon the basis of the estimation result from the channel qualityestimation function and controls the hopping frequency decision unit 44to make it perform frequency hopping while avoiding the frequencychannel which has been determined unusable.

In the Bluetooth device of the first embodiment, a new step S71 is addedas shown in a flowchart in FIG. 9, in addition to the basic operationsshown in the flowchart in FIG. 6 when the reception unit 42 receives thepacket data.

That is, when estimating the quality of the channel to be used by theBluetooth device itself by using the Active system, the Bluetooth deviceestimates each channel quality on the basis of the error rates of thepackets in communications. However, even when the Sync Error occurs, ifit is assumed that the packet to be originally transmitted cannot bereceived because of deterioration in quality of the channel which hasbeen used in the reception operation, Sync Error information can be alsoused to estimate the channel quality.

More specifically, the Bluetooth device calculates the packet error ratein the following method. The error detecting unit 48 counts the numberof times of the reception operations for each channel to update(increment) it at every time (step S71). Furthermore, when the SyncError is detected in the step S64, the number of times of the packeterrors is incremented in the step S70.

When the Header errors are detected in the step S65, the number of timesof the Header errors in the corresponding channels is incremented in thestep S70. When the data section errors are detected in the step S66, thenumber of times of the data section errors in the corresponding channelsmay be incremented in the step S70.

The procedure deciding the channel to be used adds new steps S96 to S98as shown in a flowchart in FIG. 10 in addition to the basic operationsshown in the flowchart in FIG. 8. At first, the transmission/receptioncontrol unit 43 instructs to start the operation deciding the channel tobe used (step S91), then, the hopping frequency decision unit 44 refersto the error information and field strength information stored in theerror detecting unit 48 and field strength measuring unit 47 (step S92).Next, the channel quality is estimated on the basis of the acquiredinformation to decide the channel to be used. In the flowchart in FIG.10, the step S96 calculates the packet error rates for each channel bydividing the number of times of the packet errors by the number of thetimes of the reception operations to estimate the channel quality, basedon the calculation result. Then, the number of times of the receptionoperations is cleared (step S97), and further, the number of times ofthe packet errors is cleared (step S98). After this, the channel to beused is decided (step S93). At last, the transmission/reception controlunit 43 notifies the channel to be used to the Bluetooth device on thepeer side (step S94) to terminate the operations (step S95).

That is, in the flowchart shown in FIG. 10, by dividing the number ofthe packet errors by the number of the times of the reception operationsfrom the time point when the last packet error rates of each channelwere calculated, the packet error rates of each channel are calculated.After calculating the packet error rates, the error detecting unit 48clears the data of the numbers of times of the reception operations andSync Errors. Wherein, if the number of the times of the receptionoperations from the time point when the last packet error rates of eachchannel were calculated is smaller than a predetermined value, ifaccuracy of the packet error rates based on the value is poor and if itis determined that erroneous determinations occur frequently, the errordetecting unit 48 may not calculate the packet error rates and may notclear the data to use the packet error rates calculated at the listtime. Or, the error detecting unit 48 may use the below-mentioned packeterror indexes as substitute for the packet error rates.

Japanese Patent Application No. 2003-362198 entitled ‘FREQUENCY HOPPINGRADIO DEVICE’ of the prior application by the present assignee disclosesa technique as an example of the channel quality evaluation method formeasuring the frequency by which received signal strength indication(RSSI) values exceed a prescribed threshold value to determine whetheror not the frequency exceeds a prescribed determination reference bycontinuously monitoring the RSSI values for each channel. The firstembodiment may adopt this technique. The aforementioned Japanese patentApplication No. 2003-362198 also discloses a technique as anotherexample of the channel quality evaluation method for measuring thefrequency by which the errors of the received data in the selected eachfrequency channel to determine whether or not the frequency exceeds aprescribed determination reference. The first embodiment may also adoptthis technique.

Usually, as described in the specification of the prior application,usual data section errors may be counted to grasp the packet errors.However, the Bluetooth performs a packet communication, so that it isrequired for the detection of the data errors to receive the errorcorrection codes included in the packet. This fact means that the datasection errors cannot be detected without the normal reception of thepacket. Therefore, when the data section errors are counted, thefrequency normally receiving packets capable of counting data sectionerrors of a subject to be measured becomes smaller. Accordingly, a timeneeded to complete the channel quality evaluation in a bad environmentsuch that packet synchronization is unusable becomes elongated. That is,the Sync Errors frequently occur in a bad radio wave environment suchthat packet synchronization is unusable, and as a result, the number ofreceived packets per unit time, arriving at the Header Errors inspectionstep (S65) and Header Section Errors inspection step (S66), becomessmaller. Therefore, the time, required until packets with the numberneeded to the error rate calculations in the Header Error inspectionstep (S65) and data section error inspection step (S66), becomes longer.

According to the first embodiment, the Bluetooth device focuses anattention on the Sync Errors so as to grasp packet errors to assume thatthe Sync Errors indicate no reception of the packet to be originallytransmitted and uses the result in which the Sync Errors are counted asthe number of times of the packet errors for the calculation of thepacket error rates. Accordingly, since the Bluetooth device can preventthe reduction in the number of the received packets per unit time tocalculate the packet error rates to quickly detect a change of thechannel qualities, the Bluetooth device can avoid a situation where arequired time until the end of the channel quality evaluation in theforegoing bad environment is lengthened.

Second Embodiment

Next the second embodiment will be described. In the second embodiment,when estimating the channel quality to decide the channel to be used,the Bluetooth device estimates the channel quality of the channel whichis assumed that its quality is excellent and used in the receptionoperation by calculating its packet error rate. When the packet errorrate becomes larger than the predetermined value (threshold value), itis assumed that the channel quality is deteriorated and the use of thechannel is stopped. On the contrary, the channel of which the quality isseemed to be poor and which is not used in the reception operation issequentially measured its field strength and when the field strength islowered, it is assumed that its quality becomes excellent and the usethereof is started again.

A flowchart in FIG. 11 shows the procedure deciding the use of thechannel to be used in the second embodiment. The flowchart of FIG. 11differs from that of FIG. 8 at the point that one step S93 among FIG. 8is divided into two steps S93A and S93B. Other points are the same asthose of FIG. 8. The step 93A estimates the channel quality. In the nextstep S93B, when deciding the channel to be used, with respect to thechannel currently in use, if the value of the packet error rate thereofis larger than the threshold value, the use of the channel is stopped,and with respect to the channel not in use now, if the field strengththereof is lowered then the use of the channel is started again.

When the number of channels to be used by the Bluetooth device is reduceand the mutual interference among the Bluetooth devices become notnegligible, it is needed to select a channel to be newly used amongchannels which have not been used. According to the second embodiment,the Bluetooth device can estimate the channel quality without sendingany packet to the channel which has been seemed not to be excellent inquality.

Accordingly, when deciding the reuse of the channel among the channelswhich were previously seemed to be poor in quality while minimizingincrease in power consumption resulting from the adoption of the Passivesystem, the Bluetooth device can estimate the channel quality withoutaffecting adverse effects onto the communication of the user data.

Third Embodiment

Next, the third embodiment will be explained. A flowchart in FIG. 12shows the reception procedures in the third embodiment. The step S70 inthe flowchart in FIG. 6 showing the basic reception operation proceduresstores the number of times of the reception operations for each channeland the number of times of errors for each type so as to calculate thepacket error rates in the update of error information. On the otherhand, in the step S72 of the flowchart in FIG. 12, the packet errorindex is defined as follows. Then, the Bluetooth device seems the packeterror index as the packet error rate to estimate the channel quality.Other operations are the same as those of the flowchart in FIG. 6.

(A) If any error is not found in the packets received in the receptionoperations, the packet error index is updated as follows.

‘packet error index=packet error index retroactive by one×[1−(1/B)](B ispredetermined positive number, 1/B is value of 0 to 1)’

(B) If any error is found in the packet received in the receptionoperations, the packet error index is updated as follows.

‘packet error index=packet error index retroactive byone×[1−(1/B)]+(1/B)’

In the third embodiment, the packet error index may calculate and updateby using any one of the Sync Errors, Header Errors and Data SectionErrors. For example, the packet error index can be calculated andupdated by using only the result of the Sync Errors. Or the packet errorindex can be calculated and updated by using all Sync Errors, HeaderErrors and Data Section Errors. The packet error index can be calculatedand updated by using all of the result of the Sync Errors, Header Errorsand Data Section Errors.

According to the third embodiment, the packet error rate can becalculated approximately only by storing only one variation.Accordingly, it is possible to calculate the packet error rate byminimizing a necessary calculation resource.

Fourth Embodiment

Next, the fourth embodiment will be described. In the fourth embodiment,when estimating a quality of a certain channel, the Bluetooth devicestarts to estimate the channel quality depending on a calculation resultof the packet error rate after performing receiving operations ofpackets in the corresponding channel by the predetermined number oftimes. After this, the packet rates are calculated at every packetreception operation to update estimation of the channel qualities.

The reception procedures in the fourth embodiment are shown in aflowchart in FIG. 13. In the fourth embodiment, the step S70 in thereception operation procedures shown in the flowchart in FIG. 6 arereplaced for three steps S73 to S75. Other steps are the same as thoseof the flowchart in FIG. 6. If the head of the packet data is not foundin the step S64, it shifts to the step S73. The step S73 determineswhether or not the Bluetooth device conducts the packet reception in thecorresponding channel by the prescribed number of times. The packetreception is conducted, the step S73 shifts to the step S74 and updatesestimation information of the channel quality to terminate the receptionoperations (step S69). Otherwise, the step S64 shifts to the step S75and does not update the estimation information of the channel quality toterminate the reception operations (step S69).

That is to say, in the fourth embodiment, when estimating a quality of acertain channel, the Bluetooth device starts the estimation of thechannel quality on the basis of the calculation results of the packeterror rates after performing the packet reception operations in thecorresponding channel by the number of predetermined times. After this,the Bluetooth device calculates the packet error rates at everyperformance of the packet reception operations to update the estimationof the channel quality.

According to the fourth embodiment, the packet error rate afterconducting the packet reception operations by the number ofpredetermined times, namely, after entering statistical balance can becalculated. Consequently, the channel quality can be estimated by thepacket error rate after entering the statistical balance and stablechannel quality estimation can be achieved.

Having described the case where the channel quality is estimated andupdated by using only information on the Sync Errors, the Bluetoothdevice may estimate and update the channel quality by suing anyinformation of the Sync Errors, Header Errors and Data Section Errors.The Bluetooth device can update one item of the equality estimationinformation by using any two items of information, and further, theBluetooth device can update individual items of quality estimationinformation corresponding to each error by using each item of errorinformation of the Sync Errors, Header Errors and Data Section Errors.

Fifth Embodiment

Next, the fifth embodiment will be described. In the fifth embodiment,the Bluetooth device measures the packet error rates and the fieldstrengths at idle slot time in parallel for each channel. Then, if it isnot considered that a value with high reliability could be obtained bytaking the number of times of the field strength measurements intoaccount when deciding a channel to be used, the Bluetooth device decidesthe channel to be used with the use of the packet error rates.

A flowchart in FIG. 14 shows the procedure deciding the channels to beused in the fifth embodiment. The procedure deciding the channels to beused shown in FIG. 14 is different in a point that the one step S93 inthe basic operation shown in FIG. 8 is divided into two steps S93A andS93C. Other points are the same as those of the flowchart in FIG. 8. Thestep S93A estimates the channel quality. In the next step S93C, when thechannels to be used is decided, if the number of times of the fieldstrength measurements is not sufficient, the channels to be used aredecided by using the packet error rates.

In the fifth embodiment, the Bluetooth device may decide the channels tobe used with the use of field strength information, or decide it byusing the packet error rates, and further, may decide it withcombinations of the strength information and packet error rates.

According to the fifth embodiment, it is not necessary to use a fieldstrength measurement result with low reliability in deciding the channelto be used even when reliability in channel quality estimation is low.

Accordingly, the Bluetooth device can stably decide the channel to beused, based on the channel quality estimation result with highreliability, which is estimated from communication of user data.

Sixth Embodiment

In the sixth embodiment, the field strength measurement result at idleslots and actual packet error rates of each channel are associated withone another in advance, and when estimating the channel quality from themeasurement result, the Bluetooth device determines that the quality isvery bad or good when the measured field strengths are higher or lowerthan the field strengths being the predetermined packet error rates,respectively.

A flowchart in FIG. 15 shows the procedure deciding the channels to beused in the sixth embodiment. The procedure deciding the channels to beused shown in FIG. 15 is different in a point that the one step S92 inthe basic operation shown in FIG. 8 is divided into two steps S93D andS93E. Other points are the same as those of the flowchart in FIG. 8.

The step S93D estimates the channel qualities as follows. That is, thestep S93D compares the measured field strengths with the field strengthsto be predetermined packet error rates. As a result, if the measuredfield strengths are higher, the channels are determined to be low inquality, and if the measured field strengths are lower, the channels aredetermined to be high in quality. In the next step S93E, the channels tobe used are decided on the basis of the determination result.

Having estimated the channel qualities by using only the fieldstrengths, the step S93D may estimate the channel quality with the useof the combination of the field strengths and packet error rates.

According to the sixth embodiment, the channel quality can be estimatedby taking influence of background noise on the packet error rates intoconsideration. Consequently, the Bluetooth device can estimate thechannel quality with higher reliability by taking into account theinfluence of field strengths at idle slots upon actual communications.

Seventh Embodiment

In a state in which a large number of Bluetooth devices makecommunications, if the number of channels to be used hopping operationis not sufficient, the probability of occurring interference amongdifferent Pico nets becomes higher. Therefore, it is preferable for theBluetooth devices to define the lowest limit number of channels to beused (minimum channel to be used) in AFH operations to secure thenumber.

In the seventh embodiment, the Bluetooth device calculates packet errorrates of each channel from the number of times of the receptionoperations and of the packet errors at each channel, respectively, andsequentially selects channels of the predetermined number in ascendingorder of packet error rates, namely in descending order of channelqualities, supposing that the packet error rates represent the channelqualities. In actual communications, the selected channel is used.

A flowchart in FIG. 16 shows the procedure deciding the channels to beused in the seventh embodiment. The procedure deciding the channel to beused shown in FIG. 16 is different in a point that the one step S93 inthe basic operation shown in FIG. 8 is divided into two steps S93A andS93F. Other points are the same as those of the flowchart in FIG. 8. Thestep S93A estimates the channel quality. The next step S93F selectschannels of the predetermined number in descending order of channelqualities.

According to the seventh embodiment, the lower limit value of the numberthe channels to be used even when the channel qualities are deterioratedall over the ISM band. Therefore, a plurality of Bluetooth devices canmaintain a small possibility to transmit with the same frequency whenthey transmit independently with one another in a narrow area.

Further, in the seventh embodiment, having used the packet error ratesof each channel, which have been calculated from the number of times ofthe reception operations and the number of the packet errors in eachchannel, by supposing that the packet error rates represent the channelqualities, it is also possible to use, for example, the packet errorindexes used in the third embodiment and other indexes.

Eighth Embodiment

It is necessary to be assumed that the Bluetooth device is carried by auser. Therefore, the access points of the wireless LAN beinginterference sources vary with the lapse of a time. In general, toprevent interference among access points of the wireless LAN, adjacentaccess points use frequencies different from each another. In such asituation, if the Bluetooth device now performing frequency hopping byavoiding a frequency currently used by a certain access point A iscarried to be moved to a site near another access point B, the Bluetoothdevice operates so as to also avoid the frequency currently used by theaccess point B.

In the eighth embodiment, repeated above-mentioned operations cause theusable channels not to remain. To avoid such a situation, when thequality of the channel now in use is deteriorated, it is assumed thatthe Bluetooth device has moved into an environment with a differentradio wave or regulation. Then, it becomes possible to use channelswhich have been assumed that they have bad qualities, so that theBluetooth device starts to use again the channels which have not beenused because they had been determined that they are deteriorated inquality.

A flowchart in FIG. 17 shows the procedure deciding the channel to beused in the eighth embodiment. The procedure deciding the channel to beused shown in FIG. 17 is different in a point that the one step S93 inthe basic operation shown in FIG. 8 is divided into two steps S93A andS93G. Other points are the same as those of the flowchart in FIG. 8.

That is to say, the Bluetooth device calculates the packet error rateson the basis of the error detection in packet reception operations toestimate the channel quality (step S93A). Next, in the case of decisionof a channel to be used in response to the estimated channel quality,the Bluetooth device starts to use again channels which have not beenused due to the previous decision of their deterioration in quality,when the packet error rate of the channel currently used becomes largerthan a prescribed value (step S93G).

According to the eighth embodiment, the Bluetooth device determinesstarts to use again the channels which have not been used due to theprevious determination of their deterioration in quality. Therefore, itis assumed that the Bluetooth device or the device to be an interferencesource moves to establish a new radio environment and a channel to beuse newly can be selected.

Ninth Embodiment

In the aforementioned eighth embodiment, supposing that the change inthe packet error rates accompanying by the lapse of a time is not soextreme, the possibility becomes higher, which the packet error rates inthe channels of which the packet error rates were not deteriorated somuch among channels which had been determined no to be used.

In the ninth embodiment, the Bluetooth device selects the channel tostart the use again, in ascending order of packet error rates of thechannels when the channels were brought into no longer use.

A flowchart in FIG. 18 shows the procedure deciding the channel to beused in the ninth embodiment. The procedure deciding the channel to beused shown in FIG. 18 is different in a point that the one step S93 inthe basic operation shown in FIG. 8 is divided into two steps S93A andS93H. Other points are the same as those of the flowchart in FIG. 8. Thestep S93A estimates the channel quality. In the next step S93H, in thecase of decision of a channel to be used in response to the estimatedchannel qualities, the Bluetooth device starts to use again channels inascending order of the packet error rates which have not been used dueto the previous decision of their deterioration in quality, when thepacket error rate of the channel currently used becomes larger than aprescribed value.

According to the ninth embodiment, the Bluetooth device uses thechannels in descending order of channels possible to be used in a newradio environment. Thereby, the Bluetooth device can quickly detect thechannels usable in the new radio environment.

Tenth Embodiment

In the Bluetooth device, it is defined that the Bluetooth devicefeedbacks the channel quality determination result on other party sideto its own side to take the result into account and decides the channelto be used. The reason for the above-described definition is to solvethe problem so-called the hidden terminal problem such that the use ofthe channel causes a communication quality to be deteriorated after allwhen any radio wave is not reached master side to an extent to affect oncommunications although radio waves affect on a slave side. However, onthe other hand, in a multi-vender environment, it is dangerous to fullydepend on a quality determination result brought from the other partyside.

In the tenth embodiment, the quality estimation results brought from theother party side are referred to a certain extent and when the channelto be used is decided, the quality estimation results of each channelnotified from a peer radio device are reflected to the packet errorrates calculated by itself. More specifically, the Bluetooth devicesubtracts prescribed values from each calculated packet error rate,respectively, if the quality determination results of each channelnotified from the peer radio device are excellent. And otherwise, theBluetooth device adds a prescribed value to each packet error rate. Thechannel to be used is decided on the basis of the values to which suchchanges are added.

A flowchart in FIG. 19 shows the procedure deciding the channel to beused in the tenth embodiment. The procedure deciding the channel to beused shown in FIG. 19 is different in a point that the one step S93 inthe basic operation shown in FIG. 8 is divided into three steps S93I,S93J and S93E. Other points are the same as those of the flowchart inFIG. 8.

In the step S93I, the Bluetooth device calculates the packet error rateson the basis of its own observation result to estimate the channelqualities. In the next step S93J, the quality determination results ofeach channel notified from the peer radio device are reflected to thepacket error rates calculated in the step S93I. That is, the Bluetoothdevice subtracts a fixed value α from each packet error rate calculatedin the step S93I for the channels notified to be excellent in qualityand adds a fixed value β to each packet error rate calculated in thestep S93I for the channels notified to be not excellent in quality. Thenext step S93E then decides the channel to be used, based on the packeterror rates calculated in the step S93J.

According to the tenth embodiment, the Bluetooth device can reflect thechannel quality determination result of the peer device to decide thechannel to be used. Thereby, the Bluetooth device can suppressdeterioration of communication quality caused by the interference sourceaffecting on the peer radio device. Further, since the Bluetooth devicereflects the channel quality determination result from the peer radiodevice to its own measurement result to decide the channel to be used onthe basis of the measurement result, the Bluetooth device can minimizethe deterioration in communication quality when the peer radio devicehas sent a channel quality determination result with low reliability.

The band widths of channels used in the wireless LAN are, as describedabove, wider than the channel width of the Bluetooth. Whereby, supposingthat the interference source is the wireless LAN, when the quality ofthe channel with the Bluetooth present therein becomes lower, thechannel of the Bluetooth can be estimated, which is influenced by thechannel of the wireless LAN. Therefore, when deciding the channel to beused, the Bluetooth device can assume the channels of the numberpredetermined, which are adjacent to the channels recognized to bedeteriorated in quality are simultaneously deteriorated in quality andcan decide that the channels should not be used.

Eleventh Embodiment

When the channels to be used in the AFH reduced in number, since powerexceeds antenna power per 1 MHz regulated by radio wave laws in somecountries to depart form conditions for a device allowed to be used inthe ISM band, it is needed to avoid such a situation.

In the eleventh embodiment, the Bluetooth device sends radio waves withthe power as maximum as defined in response to the number of channels ofwhich the use are determined when this number of the channels is smallerthan a prescribed number.

That is, the Bluetooth device can send a message that is ‘link managerprotocol (LMP)_incr_power_req protocol data unit (PDU) to other partybetween terminals now in communications when the radio waves become weakand can request for radio wave transmissions with further strong power.The side which has received this message intends to increase thetransmission power in response to this message. At this moment, theBluetooth device refers to the number of the channels now used in theAFH. If the number of the channels is smaller than the predeterminednumber, the Bluetooth device increases the transmission power up to thevalue, for example, the value smaller than the maximum power possible tobe transmitted by the wireless LAN module. If the number of the channelsexceeds the predetermined number, even when the module has capability tophysically sent the transmission power, the Bluetooth device sends amessage LMP_max power PDU notifying that it cannot send the radio waveswith the power more than the power defined in response to the number ofthe channels determined to be used and rejects to further increase thetransmission power.

On the contrary, if the Bluetooth device sends the radio waves with thepower stronger than the antenna power per 1 MHz defined in response tothe number of channels determined to be used, the Bluetooth device doesnot notify the power to a communication partner and decreases thetransmission power to the power defined by the number of thecorresponding channels.

The procedure deciding transmission power in the transmission unit 41 ofthe eleventh embodiment is shown in a flowchart in FIG. 20. A flowchartin FIG. 21 shows the procedure deciding the channel to be used in theeleventh embodiment.

At first, the procedure deciding the transmission power will bedescribed by referring to FIG. 20. When receiving the messageLMP_incr_power_req PDU, the Bluetooth device starts protocol processing(step S101). Firstly, it is determined whether or not the transmissionpower has reached the physical maximum power (step S102). If it hasreached the maximum power, a process not to change the transmissionpower is conducted (step S103), then, the message LMP_max_power PDU issent (step S104) and the protocol processing in the case receiving themessage LMP_incr_power_req PDU is completed (step S105).

When the step S102 determines that the transmission power has notreached the maximum power, it is determined whether or not the number ofthe channels now used in the AFH is smaller than the threshold value ofthe number of the channels (step S106). If the number is determined notto be smaller than the threshold value, the transmission power isincreased (step S107) then the protocol processing in the case ofreceiving the message LMP_incr_power_req PDU is terminated (step S105).On the contrary, if the number of the channels is determined to besmaller than the threshold value in the step S106, it is determinedwhether or not the transmission power has already reached the powerregulated by radio wave law (step S108). Then if it has reached, theaforementioned step S103 does not change the transmission power, andotherwise, the aforementioned step S107 increases the transmissionpower.

The step S96 of the flowchart shown in FIG. 21 is equivalent to theprocedure to decide the transmission power shown in FIG. 20. Theprocedure deciding the channel to be used shown in FIG. 21 is differentin a point that the one step S93 in the basic operation shown in FIG. 8is divided into two steps S93A and S93E and in a point that the step S96equivalent to the procedure deciding the transmission power shown inFIG. 20 is executed after the step S93E. Other points are the same asthose of the flowchart in FIG. 8.

That is to say, after estimating the channel qualities and deciding thechannel to be used in the steps S93A and S93E, the transmission power isdecided.

Operations of the Bluetooth device in the eleventh embodiment will bedescribed in detail as follows. As the result from the estimation of thechannel qualities, transmission approved maximum power defined from thenumber of channels determined to be used is compared with thetransmission power from the device at that time. If the radio waves areintended to be transmitted with the transmission power exceeding thetransmission approved maximum power, the transmission power is minimizedto the transmission approved maximum power. The transmission approvedmaximum power is given by, for example, A×N when the number of channelsdetermined to be used is set to N and antenna power per 1 MHz to applyto a technical standard is set to A (mW), by taking into account thefact that the band width of the channel of the Bluetooth is 1 MHz.

The Bluetooth can request for the message of LMP_incr_power_req PDU toincrease the transmission power to the peer side or for the message ofLMP_decr_power_req PDU to decrease the transmission power so as to fitinto a range less in error and possible to be demodulated (Golden Range)during communications. In the case of performance of the foregoingprocessing, when the message LMP_incr_power_req PDU is requested fromthe peer device, if acceptance of the request causes the transmissionpower to be exceeded the transmission approved maximum power, theBluetooth device may notify that it is impossible to further increasethe transmission power (LMP_max_power PDU) to the peer side and send theradio waves with the transmission approved maximum power.

In this case, the quality of a communication with the device with theLMP_max_power PDU notified thereto remains in a deteriorated statebecause the reception power does not fit into the Golden Range of thedevice. This fact indicates that the Sync Error, Header Error and datasection Error are in increased states. Then, in the channel qualityestimation systems of the foregoing each embodiment, it occurs todetermine a communication quality of a channel is in a deterioratedstate. A device with a high output, which is called class 1 among theBluetooth devices, limits the antenna power so as to make the devicematch to the technical standard. Therefore, the case of an occurrence ofsuch a state is mainly generated in the case where the distance to thedevice communicating in the presence of the interference source such asthe wireless LAN around the device becomes long gradually. In this case,since a communication distance is long, time variations of effects fromthe interference source such as the wireless LAN affected on theBluetooth communication is small and the possibility is low, whereinanother channel which has been already determined to be bad in qualityhas changed into a state good in quality. In this case, it is assumedthat operations to find out the channel which has been varied into anexcellent state among the channels which have been determined to be inbad qualities causes the communication qualities among devices to beextremely influenced. To prevent this situation, it is preferable tocontinue the use of channels as much as possible, which were previouslydetermined to be used. To achieve this situation, the Bluetooth devicemay increase, in advance, the threshold value of the packet error rate,in which the quality of the channel is determined to be bad, by thepredetermined value when making communications with the devices of whichthe transmission power is controlled so as not to exceed thetransmission approved maximum power. In this case, the distance from thepeer device is shortened again, the message of LMP_decr_power_req PDU isnotified from the peer side device and when the peer side requests thetransmission with the power less than the transmission approved maximumpower, the threshold value of the packet error rates determined to be inbad qualities may be reverted to original values. Or, if theaforementioned situations occur, the channel quality estimationoperations may be stopped at the occurrence time. In the case ofstopping the channel quality estimation operations, the distance fromthe peer device is shorten again, and the message of LMP_decr_power_reqPDU is notified from the peer side device, and the channel qualityestimation operations may be restarted when the transmission in thepower less than the transmission approved maximum power is requestedfrom the peer side.

There is the case where the received radio waves from the peer devicebecome weak and the message LMP_max_power PDU retunes as the result ofthe transmission of the message LMP_incr_power_req PDU to the peer side.At this time, in the case of setting upper limit of the transmissionpower in response to the number of the selected channels in order toavoid the transmission exceeding the transmission approved maximumpower, the meaning of this message LMP_max_power PDU includes the twocases as follows.

(1) The case in which the transmission power has reached the maximumpower allowed to be transmitted from the peer device.

(2) The case in which the transmission power has reached thetransmission approved maximum power in response to the number ofselected channels.

In the Bluetooth, since an absolute value of the transmission power fromthe peer side device cannot be known, it is not distinguished which caseof (1) or (2) is represented thorough the message LMP_max_power PDU.However, the limitation of the transmission power having thetransmission approved maximum power as the upper limit occurs only inthe class 1 device. In this case, it can be assumed that thecommunication distances among the devices become long and the variationsin time of interference from the interference source become small.Therefore, even when the Bluetooth device sends the messageLMP_max_power PDU and received the message LMP_incr_power_req PDU, theBluetooth device may continuously use the channel which has been used aslong as possible by increasing the packet error rate to be determined asa bad quality of a channel by a predetermined value or by stopping thechannel quality estimation operations as like the case of the receptionof the message LMP_incr_power_req PDU. Even when the packet error ratedetermined to be in the bad quality is increased or when the channelquality estimation operations are stopped, similarly, when thetransmission power becomes the value that the device can transmit themessage LMP_decr_power_req PDU, the packet error rate determined to bein the bad quality may be reverted to the original rate or the channelquality estimation may be started again.

According to the eleventh embodiment, even if the channel qualities ofmost of the channels in the ISM band are lowered and the number of thechannels used in the Bluetooth is reduced, the antenna power per 1 MHzcan be suppressed not more than a fixed value. Therefore, the Bluetoothdevice can avoid a situation in which the channel to be used becomes apart of the ISM band to affect adverse effects on other devices.

Twelfth Embodiment

When deciding the channel to be used, the Bluetooth device needs toalways use at least not smaller than a minimum number of channels to beused, which is defined in advance in accordance with the magnitude ofthe power to be transmitted so as to prevent transmission power per onechannel from exceeding the antenna power per 1 MHz regulated by radiolaws in some countries. At this time, The Bluetooth device sequentiallyselects channels in descending order of channel qualities estimated bypredetermined method to make communications by using the selectedchannel. During the communications, the Bluetooth device measures thechannel quality, and when the quality is deteriorated less than thepredetermined condition, the Bluetooth device stops the use of thechannel to start reuse of other channel.

Here, if the channel quality of other channel which has been started thereuse is poor in quality and if the channel quality has a level to bereused, a situation is assumed, in which the number of usable channelsbecomes smaller than the minimum number defined in accordance with themagnitude of the power to be transmitted. In the case of occurrence ofsuch a situation, the Bluetooth device restricts the number of channelsto be stopped their use and always uses not less than the minimum numberof channels defined in accordance with the magnitude of the power to betransmitted. In other words, even when there is a risk of beingdetermined that the channel quality is bad to leave adverse effects oncommunications, there is a necessity to use channels of the number notexceeding the maximum value of the antenna power per 1 MHz intransmission power in the case of keeping the transmission power.

A flowchart in FIG. 22 shows the procedure deciding the channel to beused in the twelfth embodiment.

The procedure deciding the channel to be used shown in FIG. 22 isdifferent in a point that the one step S93 in the basic operation shownin FIG. 8 is divided into two steps S93A and S93K and in a point thatthe steps S97 and S98 to decide the transmission power are executedafter the step S93K. Other points are the same as those of the flowchartin FIG. 8.

That is to say, after the steps S93A and S93K estimate the channelquality and temporarily decide the channel to be used, the steps S97 andS98 decide the transmission power. At first, it is determined whether ornot the number of channels to be used is not smaller than the numberpredetermined in accordance with the magnitude of the power to betransmitted (step S97). If the number is not smaller than thepredetermined number, the Bluetooth device notifies the channel to beused to the Bluetooth device located on the peer side (step S94) tocomplete its own operations (step S95). Otherwise, the number of thechannels to be used is increased until the number reaches the numberdefined in accordance with the magnitude of the power to be transmitted(step S98) to notify the channel to be used to the Bluetooth device onthe peer side (step S94) and the operations are completed (step S95).

According to the twelfth embodiment, even when the channel qualities inmost of the ISM band are deteriorated and the number of channelspossible to be used by the Bluetooth device is reduced, the antennapower per 1 MHz can be suppressed not more than the fixed value withouthaving to limit the transmission power extremely. Therefore, theBluetooth device can prevent the situation in which the channels to beused from becoming a part of the ISM band to affect adverse effects onother devices.

The further detailed operations of the Bluetooth device in the twelfthembodiment are described as follows.

According to the result of estimation of channel qualities, thetransmission approved maximum power defined from the number of channelsdetermined to be used is compared with the transmission power from theBluetooth device at this time. If the Bluetooth device intends totransmit the transmission power exceeding the transmission approvedmaximum power, the Bluetooth device increases the number of the channelsto be used so that it can transmit the transmission power within thetransmission approved maximum power. The transmission approved maximumpower is given by, for example, A×N when the number of channelsdetermined to be used is set to N and antenna power per 1 MHz to applyto a technical standard is set to A (mW), by taking into account thefact that the band width of the channel of the Bluetooth is 1 MHz. Thetotal number of channels to be newly added becomes B−A×N when antennapower is set B (mW).

The Bluetooth can request for the message of LMP_incr_power_req PDU toincrease the transmission power to the peer side or for the message ofLMP_decr_power_req PDU to decrease the transmission power so as to fitinto Golden Range during communications. In the case of performance ofthe foregoing processing, when the message LMP_incr_power_req PDU isrequested from the peer device, if acceptance of the request causes thetransmission power to be exceeded the transmission approved maximumpower, the Bluetooth device continues the use of the channel of whichthe quality has determined to be bad, in response to the request. Thisfact indicates that the Sync Error, Header Error and data section Errorremain in increased states. In the method for deciding channel to beused adopted to the present invention, the forgoing fact means that itis continuously generated to select a channel to be newly used fromamong channels of which the qualities are determined to be bad. By theway, a device with a high output, which is called class 1 among theBluetooth devices, limits the antenna power so as to make the devicematch to the technical standard. Therefore, the case of an occurrence ofsuch a situation is mainly generated in the case where the distance tothe device communicating in the presence of the interference source suchas the wireless LAN around the device gradually lengthened. In thiscase, a communication distance is long. Thus, time variations of effectsfrom the interference source such as the wireless LAN affected on theBluetooth communication is small and the possibility is low, in whichanother channel which has been already determined to be band in qualityhas changed into a state excellent in quality. In this case, it isassumed that operations to find out the channel which has been variedinto an excellent state among the channels which have been determined inbad qualities causes the communication qualities among devices to beextremely influenced. To prevent this situation, it is preferable tocontinue the use of channels as much as possible, which were previouslydetermined to be used. To achieve this situation, the Bluetooth devicemay increase the threshold value of the packet error rate by thepredetermined value, in which the quality of the channel is determinedto be bad, by the predetermined value when making communications withthe devices of which the number of the channels were increased so as notto exceed the transmission approved maximum power. In this case, thedistance from the peer device is shortened again, the message ofLMP_decr_power_req PDU is notified from the peer side device, when thetransmission approved maximum power can be satisfied even if the channelof which the quality is determined to be very bad is not selected, theBluetooth device may put back the threshold value of the packet errorrate, in which the quality of the channel is determined to be bad.

Alternatively, the estimation of channel quality may be stopped whenthis takes place. In this case, the distance from the peer device isshortened again. The peer device therefore generates the message,LMP_decr_power_req PDU. The channel quality estimation operations may berestarted when the transmission approved maximum power can be satisfiedeven if the channel of which the quality is determined to be very bad isnot selected.

In the case where the Bluetooth device selects channels includingchannels which have been bad in quality so as to satisfy thetransmission approved maximum power, there is the case where thereceived radio waves for the message LMP_max_power PDU from the peerdevice become weak and the fact that the channels which have beendetermined to be very bad in quality by the Bluetooth device inaccordance with the result of the estimation of the channel quality bythe peer side device is notified as the result of the transmission ofthe message LMP_incr_power_req PDU to the peer side. The meaning of thisdetermination of excellent in quality includes the two cases as follows.

(1) The case in which the hidden terminal for the peer side device ispresent and the peer side device determined the quality is excellent.

(2) The case in which the transmission approved maximum power cannot besatisfied if the Bluetooth device cannot enter a hopping sequence whileincluding the channels which have been determined to be bad in quality.

In the Bluetooth, since an absolute value of the transmission power fromthe peer side device cannot be known, it is not distinguished which caseof (1) or (2) represents the determination that the quality is good bythe peer side device different from the determination that the qualityis bad by this side device. However, if this side device does not selectthe channel in accordance with the determination by the peer sidedevice, the peer side device cannot satisfy the transmission approvedmaximum power.

Each embodiment mentioned above has the following feature in comparisonwith the invention disclosed by Japan Patent No. 3,443,094.

(1) With respect to the method for estimation channel quality, each ofthe embodiments can solve a variety of hard problems which occur incalculation of statistic information on the packet error rates.

(2) With respect to the method for selecting channel to be used, each ofthe embodiments can adopts measures for securing a minimum number ofchannels so as to reduce possibility of interferences among theBluetooth devices, measures for corresponding to the case of change inradio wave environment, and the Passive system for compensating theproblem that information to estimate qualities of channels not used inthe Active system.

(3) With respect to the association between the AFH and the channelselection, each of the embodiments can solve the problem that when thenumber of channels to be selected becomes small, the antenna power per 1MHz is increased then it becomes impossible to satisfy the conditions ofthe device allowed to be used in the ISM band.

The foregoing radio communication terminals in each embodiment and theeffects given by the terminals are organized as follows.

(1) The radio communication terminal of the first embodiment receives apacket by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.When the head of the packet could not be detected in the receptionoperations, the terminal cannot receive the packet to be originallyreceived because of deterioration in channel quality to consider it as apacket error. When estimating a channel quality of a certain channel,the terminal calculates the packet error rates for each channel on thebasis of the number of times the reception operations performed for eachchannel and the number of times of the packet errors to estimate thechannel qualities by using the corresponding packet error rate.

The radio communication terminal having such a configuration provides aneffect capable of quickly estimating the channel qualities by the methodfor estimating channel qualities in the Active system.

(2) The radio communication terminal of the second embodiment receives apacket by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.The terminal calculates the packet error rates to estimate the channelqualities for the channels which are assumed that of which the qualitiesare good to be used in the reception operations. And the terminalsequentially measures the field strengths by idle slots to estimate thechannel qualities for the channels which are assumed that of which thequalities are bad not to be used in the reception operations.

The radio communication terminal having such a configuration canprovides an effect capable of estimating the channel qualities withoutaffecting adverse effects on communications for user data when selectingthe channel to be newly used from among the channels which werepreviously assumed that of which the qualities were bad and which werenot used up until now.

(3) The radio communication terminal of the third embodiment receives apacket by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.The terminal stores the packet error indexes for each channel to updatethe index as follows when any error was not found in the packets in thereception operations: packet error index=packet error index retroactiveby one×[1−(1/B)] (B is a predetermined positive number; 1/B is a valuein a range of 0-1). When any error was found in the packets received inthe reception operations, the packet error index is updated as follows:packet error index=packet error index retroactive byone×[1−(1/B)]+(1/B). The terminal then estimates the channel qualitiesby assuming that the updated packet error index is the packet errorrate.

The radio communication terminal having such a configuration cancalculate the packet error rate approximately, so that the terminal canproduce an effect capable of calculating the packet error rate byminimizing a necessary calculation resource.

(4) The radio communication terminal of the fourth embodiment receives apacket by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.When estimating a channel quality of a certain channel, the terminalstarts to estimate the channel quality in accordance with thecalculation result of the packet error rate after performing the packetreception operations by the number of predetermined times, and afterthis, calculates the packet error rates at every packet receptionoperation to update the estimation of the channel qualities.

The radio communication terminal having such a configuration canestimate the channel qualities by the packet error rates after enteringthe statistic balance and can produce an effect capable of stablyestimate the channel qualities.

(5) The radio communication terminal of the fifth embodiment receives apacket by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.The terminal individually evaluates quality performance for each channelon the basis of the packet error rates and measured field strengths foreach frequency channel selected by the hopping frequency decision unit.And when determining whether or not the corresponding frequency channelsare usable on the basis of the estimation result for the frequencychannels targeted as the estimation of the channel quality, the terminalselects to use either the channel qualities estimated from the packeterror rates or from the measurement results of the field strengths bytaking the frequency of the measuring slots in measuring the fieldstrengths into consideration.

The radio communication terminal having such a configuration produces aneffect capable of deciding the channel to be used in accordance with thechannel quality estimation result which is estimated from communicationsof user data and is high in reliability even when there are not enoughidle slots because of making communications high in load and thereliability of channel quality estimation based on the measurementresult of the field strengths is low.

(6) The radio communication terminal of the sixth embodiment receives apacket by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.The results of sequentially performing the field strength measurement bythe idle slots and the packet error rates can be measured as the resultof actual communications by using each channel are associated with oneanother. And when estimating the channel qualities from the measurementresults for each selected frequency channels, respectively, the terminaldetermines that the quality is bad if the observed field strength ishigher than the field effect being the predetermined packet error rate,and otherwise the terminal determines that the quality is good.

The radio communication terminal having such a configuration can decidethat the quality is assumed to be bad or good on the basis of the resultof the field strength measurement by measuring the relationship betweenthe field strength measurement result though the idle slot and theactual packet error rate, so that the terminal can estimate the channelquality with high reliability.

(7) The radio communication terminal of the seventh embodiment receivesa packet by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.When deciding the channel to be used in response to the channelqualities estimated by the predetermined method, the terminal assumesthat the channel qualities are the packet error rates to compare thepacket rates of each channel with one another and uses the channels ofthe predetermined number in ascending order of packet error rates,namely in descending order of channel qualities.

The radio communication terminal having such a configuration can producean effect capable of minimizing the possibility of transmissions withthe same frequency when a plurality of the Bluetooth devices performstransmissions.

(8) The radio communication terminal of the eighth embodiment receives apacket by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.When calculating the packet error rates on the basis of the errordetection in the packet reception operations to estimate the channelqualities and deciding the channel to be used in response to theestimated channel quality, if the packet error rate of the channel beingused now becomes not less than the predetermined value, the terminalstarts reuse of the channel which has not been used due to thedetermination that the quality was deteriorated previously.

The radio communication terminal having such a configuration assumesthat the Bluetooth device or the device being the interference sourcemoves to produce a new radio environment, and produces an effect capableof selecting the channel to newly start the use thereof.

(9) The radio communication terminal of the ninth embodiment receives apacket by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.When calculating the packet error rates on the basis of the errordetection in the packet reception operations to estimate the channelqualities and deciding the channel to be used in response to theestimated channel quality, if the packet error rate of the channel beingused now becomes not less than the predetermined value, the terminalstarts reuse of the channel which has not been used due to thedetermination that the quality was deteriorated previously. At thistime, the channels started the use thereof are uses in ascending orderof packet error rates at the time when the channels were brought into nouse.

The radio communication terminal having such a configuration uses thechannels in descending order of high possibilities capable of using innew radio environment then can quickly detect the channels usable in thenew radio environment.

(10) The radio communication terminal of the tenth embodiment receives apacket by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.When calculating the packet error rates on the basis of the errordetection in the packet reception operations to estimate the channelqualities and deciding whether or not the corresponding frequencychannel is usable on the basis of the estimation result of the frequencychannel targeted as the estimation object, if the results of qualityestimation of each channel notified from the peer radio device are good,the terminal subtracts the predetermined first values from each packeterror rate, respectively. And otherwise, the terminal adds thepredetermined second values to each packet rate, respectively, anddecides the channel to be used by using the results.

The radio communication terminal having such a configuration cansuppress deterioration in communication quality caused by theinterference source which does not affect on the terminal itself butaffects on the peer radio device. The terminal can minimize thedeterioration in the communication quality when the peer radio devicehas sent a channel quality estimation result with low reliability.

(11) The radio communication terminal of the eleventh embodimentreceives a packet by sequentially using a plurality of frequencychannels in accordance with instructions from the hopping frequencydecision unit. As the result of deciding the channel to be used, if thenumber of channels determined to be used is smaller than thepredetermined number, the terminal transmits radio waves through thepower defined in response to the number of channels determined to beused as the maximum value.

The radio communication terminal having such a configuration can avoidthe situation where the channels to be used become a part of the ISMband to affect adverse effects on other devices.

(12) The radio communication terminal of the twelfth embodiment receivesa packet by sequentially using a plurality of frequency channels inaccordance with instructions from the hopping frequency decision unit.As the result of deciding the channel to be used, even if the number ofchannels determined to be used is smaller than the number defined by thetransmission power at this time, the terminal uses the channels of thenumber defined by the transmission power.

The radio communication terminal having such a configuration can avoidthe situation where the channels to be used become a part of the ISMband to affect adverse effects on other devices.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A semiconductor device comprising a firstcontroller, wherein the first controller includes: a first unitconfigured to select one frequency channel from a plurality of frequencychannels, a reception unit configured to receive packet data via theselected frequency channel, and count the number of operations toreceive the packet data via the selected frequency channel; an errordetection unit configured to detect a packet synchronization error and asynchronization detection error at the selected frequency channel, andto sum up the number of packet synchronization errors and the number ofsynchronization detection errors, a second controller configured tocalculate a packet error rate for the selected frequency channels basedon the number obtained by summing the number of packet synchronizationerrors and the number of synchronization detection errors, and thenumber of operations; and a transmission unit configured to transmitpacket data by using the selected frequency channel.
 2. The deviceaccording to claim 1, wherein the second controller configured tocontrol selection operation of the first unit based on the packet errorrate.
 3. The device according to claim 2, wherein the second controllerconfigured to determine whether a frequency channel is usable or notbased on the result of evaluation of the packet error rate, and controlselection operation of the first unit to avoid a frequency channel whichis determined as unusable.
 4. The device according to claim 2, whereinafter the second controller calculated the packet error rate, the errordetection unit configured to reset the number of operations to receivethe packet data and the synchronization detection errors.
 5. The deviceaccording to claim 2, wherein if the number of operations is lower thana predetermined number, the second controller configured not tocalculate the packet error rate, and the error detection unit configurednot to reset the number of operations to receive the packet data and thesynchronization detection errors.
 6. The device according to claim 2,wherein the synchronization detection error indicates that a Sync Wordof a preset pattern be not able to detect within a predetermined timeperiod.
 7. The device according to claim 6, wherein the packetsynchronization error is a header error or a data section error.
 8. Thedevice according to claim 7, wherein the header error indicates that anerror is detected in header error inspection, and the detected errorexceeds ability of an error correction code, and the data section errorindicates that an error is detected in data section error inspection,and the detected error exceeds the ability of the error correction code.9. A semiconductor device comprising a controller, wherein thecontroller configured to select one frequency channel from a pluralityof frequency channels, receive packet data via the selected frequencychannel, count the number of operations to receive the packet data viathe selected frequency channel detect a packet synchronization error anda synchronization detection error at the selected frequency channel, sumup the number of packet synchronization errors and the number ofsynchronization detection errors, calculate a packet error rate for theselected frequency channels based on the number obtained by summing thenumber of packet synchronization errors and the number ofsynchronization detection errors, and the number of operations, andtransmit packet data by using the selected frequency channel.
 10. Thedevice according to claim 9, wherein the controller configured todetermine whether each frequency channel is usable or not based on thepacket error rate, and select one frequency channel to avoid frequencychannels which are determined as unusable.
 11. The device according toclaim 10, wherein after the selection of the frequency channel, thecontroller configured to reset the number of operations to receive thepacket data and the synchronization detection errors.
 12. The deviceaccording to claim 11, wherein if the number of operations is lower thana predetermined number, the controller configured not to calculate thepacket error rate, and not to reset the number of operations to receivethe packet data and the synchronization detection errors.
 13. The deviceaccording to claim 9, wherein the synchronization detection errorindicates that a Sync Word of a preset pattern be not able to detectwithin a predetermined time period.
 14. The device according to claim13, wherein the packet synchronization error is a header error or a datasection error.
 15. The device according to claim 14, wherein the headererror indicates that an error is detected in header error inspection,and the detected error exceeds ability of an error correction code, andthe data section error indicates that an error is detected in datasection error inspection, and the detected error exceeds the ability ofthe error correction code.